This invention relates generally to a fastener assembly for securing a flexible roofing membrane to an underlying roof structure which is made up of an upper layer of insulation and a lower deck.
In certain modern roofing installations for commercial buildings, a layer of insulation is secured to the deck of the roof and then is covered with sheets of flexible material such as polyvinyl chloride. Adjacent margins of adjacent sheets are sealed together in overlapping relationship and thus the sheets form a sealing membrane over the insulation.
The sheets which form the membrane are secured to the insulation and the underlying roof deck at spaced locations by fastener assemblies which are spaced along the margins of the sheets. Each fastener assembly comprises a washer-like disc made of plastic and further comprises a screw adapted to thread into the roof deck to cause the disc to clamp the membrane downwardly against the insulation.
A fastener assembly of the same general type as the fastener assembly of the invention is disclosed in Reinwall et al U.S. Pat. No. 4,630,984. The plastic disc of that fastener assembly includes a central hub which penetrates the insulation and further includes a series of angularly spaced strengthening ribs which extend radially along the underside of the disc to reinforce the disc against upward flexing.
One of the problems presented by membrane-type roof installations involves uplift forces which tend to cause the membrane to billow upwardly. Wind blowing across the roof creates a negative pressure on the upper side of the membrane and, as a result, the membrane billows upwardly. While a fastener assembly of the type disolosed in the aforementioned Reinwall et al patent is capable of adequately resisting the vertical force component of the billowing membrane, the horizontal force component tends to tear the membrane edgewise away from the hub of the clamping disc. Eventually, the membrane either rips completely away from the fastener assembly or is formed with unacceptably large tears.